1. Field of the Invention
The present invention relates to a mobile communication system, a switching center server and an additional service providing method used for the same, more specifically to a mobile communication system, a switching center server and an additional service provided from them in SIP (Session Initiation Protocol) sequence.
2. Description of the Related Art
Recently, cellular phones, which are an example of a mobile communication service, have been significantly popular, popularizing the 3GPP: 3rd Generation Partnership Project service, the WLAN: Wireless Local Area Network service and the like.
There is a trend of integrating all these systems into the IP (Internet Protocol) network. IMS (IP Multimedia Subsystem) is a service for providing an IP based multi media service without depending on the 3rd generation cellular phone or the wireless LAN, enabling not only providing an IP based service but also connecting with the PSTN (Public Switched Telephone Network) or the Internet and providing a service. In the IMS network, the SIP is used as a controlling protocol.
The 3rd generation cellular phone network includes the CS (Circuit Switched) domain that uses a conventional circuit switching network and the PS (Packet Switched) domain that uses a packet switching network. The IMS is a subsystem that is built on the PS domain, thus, the IMS is independent of the CS domain. In order to accommodate the CS service into the IMS network, the CS service needs to be converted into the PS service, i.e., a signal protocol in the CS domain needs to be converted into SIP in the PS domain.
In the above-mentioned conventional method, however, there is a difference between the calling methods. In the CS call processing between the wireless LAN and the 3rd generation cellular phone, the call processing node at the wireless LAN side is the CSCF (Call Session Control Function), which is different from the MSC (Mobile Switching Center) that is the call processing node at the 3rd generation cellular phone side.
As a technique for enabling the signal protocol of the above-mentioned CS domain to be converted into the SIP of the PS domain, a technique for converting a signal protocol into the SIP signal to perform handover between different radio transmissions (for example, see Japanese Patent Laid-Open No. 2007-060181), and so on, is disclosed.
As the additional service in the 3rd generation cellular phone service, a service of the GSM (Global System for Mobile communication) standard [CF (Call Forwarding), CW (Call Waiting), CB (Call Barring, CLIR (Calling Line Identification Restriction) and so on and a service in IN (Intelligent Network) method are used. The IN method is a network intending to realize addition and extension of a service without changing a software program of an exchange by separating service controlling, management and maintenance of data relating to a service from the exchange into another node.
The above-mentioned CB and CLIR services, however, cannot be provided for the 3rd generation cellular phone service that is accommodated in the IMS network. The existing SIP sequence at a normal occasion is shown in FIGS. 8 to 10.
As shown in FIGS. 8 to 10, in the existing 3rd generation cellular phone system, a normal-sequence and a semi-normal-sequence signal can be determined in the MSC (Mobile Switching Center) (see, e1 to e21 in FIG. 8, e22 to e44 in FIG. 9 and e45 to e56 in FIG. 10)
In the IMS network that is included in the IP system, however, the MSC-IWF (Mobile Switching Center-Inter Working Function) only converts a signal protocol from the 3rd generation cellular phone service into the SIP, and unless the CSCF that is a device in the IMS network receives an INVITE signal [connection request (request to establish a session)], it cannot be determined.
Therefore, determination of a signal and sending timing differs between the two systems as mentioned above. Thus, the timing to send Call Proceeding (e12 in FIG. 8) for determining a normal-sequence signal becomes important. In an existing SIP sequence, however, Call Proceeding (e12 in FIG. 8) is sent from the MSC-IWF to the RNC (Radio Network Controller) in response to the 100 Trying (a temporal response representing that it is under trial), thus, under the CB or the CLIR that are a semi-normal-sequence service, a signal needs to flow in such a flow as a SETUP signal is transferred from the RNC to MSC-IWF (e9 in FIG. 8) and a RELCOMP signal (Release Complete Message) is sent from the MSC-IWF to the RNC {see, “Call Barring (CB) Supplementary Service-Stage 3” [3GPP TS24. 088 V6.0.0 (2003-03)] (Non-Patent Document 1) and “Line Identification Supplementary Service-Stage 3” [3GPP TS24.081 V6.0.0 (2004-12)] (Non-Patent Document 2)}.
In the conventional additional service, however, the Call Proceeding signal (e12 in FIG. 8) is inserted between the SETUP signal (e9 in FIG. 8) and the RELCOMP signal, which leads to a problem in that a signal cannot be mapped.
FIGS. 11 to 13 show the SIP sequence by 183 signal determination at a normal occasion (see f1 to f18 in FIG. 11, f19 to f42 in FIG. 12, f43 to f56 in FIG. 13).
As a solution of the above-mentioned problem in the existing SIP sequence shown in FIGS. 8 to 10, when the MSC-IWF receives the 183 Session Progress signal (progress of the session) (f26 in FIG. 12) in a normal occasion and changes to send Call Processing (f27 in FIG. 12) to the RNC as shown in FIGS. 11 to 13, the processing can be normally performed on the CB or the CLIR that would not be subjected to signal mapping in the existing SIP sequence shown in FIGS. 8 to 10.
In the case of normal-sequence operations, however, authentication, concealment, setting up and so on need to be performed on the incoming side by the time when 183 Session Progress (f26 in FIG. 12) is received. That leads to a problem in that a delay occurs. That means that a delay occurs each time a user uses a service, which will degrade the service.
Then, an object of the present invention is to provide a mobile communication system that can provide the CB and the CLIR services that solve the above-mentioned problems without affecting an existing service, a switching center server and an additional service providing method used for the same.